The sine wave filter is a special device in the entire motor drive system. In order to enable the motor to transition from fully closed to open in a short time fully, the sine wave filter plays a great role. Next, let us understand the working principle of this special device and the precautions during use.
What Is Sine Wave Filter-sourced: LTEC
Sine wave filters are mainly used to convert the output voltage in the inverter into a sinusoidal voltage with low residual ripple. It is a low-pass filter. Mainly used with high-speed drives, sine wave filters can reduce interference signals generated by the cables in the inverter.
While protecting the motor from excessive voltage spikes and overheating, it can attenuate voltage peaks, improve electronic compatibility, and extend the service life of the equipment. This filter is generally composed of single-phase or three-phase reactors and capacitors connected in delta or wye.
Before learn about sine wave filters, you need to know the following tips:
Voltage drop
Voltage drop-sourced: allaboutcircuits
Voltage drop refers to the voltage drop across a sine wave filter that reduces the maximum available torque of the motor. You must consider voltage drop when sizing the motor and drive. If the power is kept constant at a power system frequency of 50 Hz and the drive is rated for 50 Hz, reducing the motor voltage will result in an increase in current.
Motor cable length
Motor cable length-sourced: mb-drive-services
When sizing the motor and drive in your own power system, you need to consider the length of the motor cable. Although the cable length between the sine wave filter and the motor is not controlled, longer motor cables will result in additional voltage drop.
Peak voltage
Peak voltage-sourced: learningaboutelectronics
When using a sine wave filter, the phase-to-phase peak voltage is approximately 1.5 × UN.
Bearing current
Bearing current-sourced: motioncontroltips
Sine wave filters reduce both circulating and shaft-grounding bearing currents.
What Is dV and dt-sourced: celduc-relais
The delta in dV/dt means "change", which is the distortion and amplification of voltage spikes over the length of the wire. Sine wave filters can eliminate such dV/dt effects, which are the voltage increment (Δ) / time increment (Δ) phenomenon. The longer the wire from the inverter to the motor, the greater this effect will be.
How Motor Drives Work-sourced: electrical-engineering-portal
Generally, if a motor using AC power wants to start or stop smoothly, it needs a special power supply to provide the corresponding power. If the motor is forced to switch from fully on to fully off in a short period of time, it will cause excessive stress on the equipment. Therefore, the motor needs power to start and stop gradually. When the motor is running, the sine wave filter can adjust the torque and speed well to adapt to various mechanical loads.
What Is Variable Frequency Drive (VFD)-sourced: realpars
A variable frequency drive is an electronic converter. It provides variable speed and torque to a motor for gradual starting and shutting down. A variable frequency drive generates a specific current and delivers it to the motor to control the frequency and speed of the motor.
Variable frequency drives are becoming more and more popular in a variety of industries to control the speed and torque of motors. In addition to being low-cost, it can be applied to a variety of high-power applications and can improve the efficiency of various energy sources.
What Are The Functions Of Sine Wave Filters-sourced: wikimedia
The main function of the sine wave filter is to eliminate the harmful side effects of transistor switching by converting the PWM voltage into a sine wave. It can protect the motor from high voltage peaks, bearing current overheating, and cable ringing. Not only is the structure compact, but it can also be easily connected to modern integrated systems.
The main benefits of applying sine wave filters are:
Adapt to different mechanical loads
Sine wave filters can smooth the square wave signals generated by the inverter and convert them into sine wave waveforms almost perfectly. This can adapt to the changes in different speed and torque operations and different mechanical loads.
Extend motor life
Extend motor life-sourced: gesrepair
Square wave pulses in the power system will cause voltage spikes in the motor, which will produce harmonic distortion and destroy the shape of the PWM output. This will cause excessive stress and loss of efficiency. Therefore, sine wave filters can adjust such problems well and increase the life of the equipment.
Improve system efficiency
Improve system efficiency-sourced: softwebsolutions
Sine wave filters can adjust the harmonic distortion generated by the motor into a sine wave waveform almost perfectly, so that almost all power can be converted into useful work, thereby reducing losses and improving the efficiency of the entire system.
Reduce noise and radiation
Sine wave filters can reduce the high-frequency signals output by the inverter to reduce living room noise and reduce the radiation caused by the equipment.
During use, the sine wave filter can block the switching frequency harmonics and high frequency components (2kHz and above) in the inverter output, but also allow the fundamental voltage (0-90Hz) to pass. By eliminating the voltage spike ringing and reflection that appear on the motor terminals of long lead cables, the sine wave filter can provide high-quality power with low total harmonic distortion to the motor.
If a sine wave filter is not used with a frequency converter, the entire system may have the following problems:
Voltage spikes
Voltage spikes-sourced: quoracdn
The square wave pulses generated by the frequency converter contain a certain proportion of voltage overshoot. This will cause voltage spikes in the system, which will damage the motor.
Excessive stress
The output of the frequency converter also produces harmonic distortion. This harmonic distortion will destroy the shape of the PWM output. If this harmonic distortion is not filtered out, it will damage the equipment in the form of heat, causing excessive stress on the motor windings and reduced efficiency.
Bearing currents
Bearing currents-sourced: est-aegis
Without a sine wave filter, the motor current will produce grooves or bearing currents. This bearing current will melt tiny pits in the motor. Over time, this current will cause bearings to break and equipment to fail.
Before choosing a sine wave filter for your motor system, you need to consider the following factors:
Rated voltage and current
Rated voltage and current-sourced: squarespace
Generally, the rated current and duty cycle of the motor determine the size of the filter. When choosing a sine wave filter, the rated current of the filter should be equal to or greater than the rated current of the motor, so that the rated current and duty cycle of the motor drive are compatible.
Frequency
Frequency-sourced: groschopp
Frequency is an important factor in choosing a sine wave filter. It includes the supply frequency, switching frequency, and motor frequency.
- Supply frequency
In an AC network, the frequency of the current is usually 50Hz or 60Hz. Depending on the voltage and frequency characteristics of your capacitor, the filter you choose can operate at a higher frequency, but the input voltage will be reduced.
- Switching frequency
The switching frequency is directly related to the power loss of the inverter. A higher switching frequency increases the switching losses of the semiconductor, which causes the motor drive to heat up. A good sine wave filter can reduce the noise level of the motor while reducing the motor harmonic currents and the temperature of the motor, avoiding motor losses.
- Motor frequency
The motor frequency of the inverter determines the speed of the motor. Therefore, the resonant frequency of the sine wave filter is at least 2.5 to 3 times lower than the switching frequency of the motor driver.
- Driver settings
If the motor driver is not set up correctly, the use of a sine wave filter may cause damage. Try not to use a low switching frequency. And adjust the output frequency level of the motor driver. Automatic frequency adaptation mode is prohibited.
Voltage drop considerations
Voltage drop considerations-sourced: diodeled
When determining the size of the motor driver, the voltage drop across the sine wave filter must be considered. At a constant motor power level, if the motor current exceeds the rated current, the motor torque will be limited or reduced. Therefore, before determining the size of the motor driver, the impact of voltage drop should be considered.
Every time you use a drive device, the speed, noise, and load of the drive are issues you need to consider. Sine wave filters can help you deal with these issues. In addition, it can also prevent equipment failure or damage. If you have any subsequent questions about filters, you are welcome to consult us!
